Methods to determine the affinity of heavy metals for the chemically extracted carrier phases in soils

A new index is proposed to determine the affinity of heavy metals (HM) to their carrier phases (AHM-fraction), which, in contrast to the traditional index CHM = 100 CHM-fraction/CHM-soil, considers the sum of all metals in the fraction as a share of the bulk content of all HM in the soil. The metal has affinity for the given phase if AHM-fraction > 1; vice versa, the affinity is absent if AHM-fraction < 1. Comparison of the affinity series of metals for a certain phase based on two indices revealed their discrepancy in most cases. The new index can take into consideration the discrepancy in affinity of the given metal for phases extracted by different strength reagents. The effect of the new indicator was tested on several contaminated soils: Haplic Chernozem, Stagnic Phaeozems, and Calcaric Fluvic Arenosol, as well as on two Spolic Technosols. Compared with the index CHM, the results of the new analysis of contaminated soils with the ATM fraction demonstrated that the Zn content in Calcaric Fluvic Arenosol is decreased considerably due to its low buffer capacity. Since the content of organic matter in Calcaric Fluvic Arenosol is insignificant, only organophile elements, such as Cu and Pb, can make up complexes with organic ligands, in contrast to the fixation of Ni and Mn by organic matter in Chernozems. Due to the low buffering capacity of Calcaric Fluvic Arenosol, the mobile forms of Cd and Zn increased, and these forms of Cr decreased. Therefore, the low buffering soil cannot fix Cd and Zn. Increase in contamination in Spolic Technosols (approximate permissible concentration, APC > 5) as compared to the index CHM, the value of the AHM-fraction of metals in the residue (except for cadmium) increased. In addition, the share of Pb and Cu increases in the organic matter. Thus, the use of a new indicator-the affinity of heavy metals to the carrier phases showed their advantage over the traditional index CHM.